Effects of solid content on the phase assemblages, mechanical and dielectric properties of porous α-SiAlON ceramics fabricated by freeze casting

Abstract

Porous Y-α-SiAlON ceramics were prepared by freezing camphene-based suspensions at 0°C and subsequently sintering at 1900°C for 1h. The effects of solid loading content in the suspensions on porosities and formation of α-SiAlON as well as mechanical and dielectric properties of the porous ceramics were investigated. An XRD analysis performed on sintered samples indicated that the α-SiAlON did not fully form in the sample with initial solid loading content of 10vol%, due to the high porosity of 90vol% and interconnected pore of the green body. With the increase of initial solid loading content from 10vol% to 30vol%, the porosity decreased from 62.3% to 23.1% and the average pore size decreased from 19μm to 8μm. As a result, the flexural strength increased significantly from 72.4MPa to 190.2MPa, fracture toughness increased from 1.20MPam1/2 to 3.48MPam1/2, as well as the dielectric constant increased from 3.3 to 6.3. The dielectric loss (tanδ) of obtained material varied between 1.4×10−2 and 2.8×10−2, which did not depend on the porosity of samples.